Riot police gather at Thai airport

Riot police are once again gathering near Bangkok's international airport where thousands of protesters are camped out demanding the Government resign.

Eyewitnesses say about 60 police officers have assembled a block or so away from the main terminal at Suvarnabhumi international airport.

Senior offices have been trying to negotiate with the leaders of the People's Alliance for Democracy (PAD) to end their occupation of the site, which has grounded hundreds of flights and stranded thousands of passengers.

Local media organisations are reporting that the police will start with a mild approache but could resort to severe tactics.

"We are asking them to allow the airport to resume operations," Lieutenant-General Suchart Muenkaew, the chief police negotiator, told reporters.

"We will keep talking, but if it fails we will take other steps. The last step will be to disperse them."

A dozen ambulances are on standby near the terminal.

Last month the police used tear gas and smoke bombs to try to disperse the group when it surrounded the national parliament, killing a young woman.

Thai Prime Minister Somchai Wongsawat has sacked his national police chief, fuelling speculation that the Government is preparing to crack down on the protesters.

General Patcharawat Wongsuwan, who was moved to an inactive post, had resisted previous orders to crackdown on the street protesters who began a "final battle" to unseat the Government on Monday, Thai media reported.

"The removal was the result of his performance during this current crisis," Government spokesman Nattawut Saikuar told NBT television a day after Mr Somchai declared a state of emergency to end the crippling airport sieges.

The University of the Thai Chamber of Commerce said if the political turmoil and airport closures go on for another month, it would cost the economy up to 215 billion baht ($US6 billion).

PAD began a "final battle" on Monday to unseat the Government which it accuses of being a pawn of former leader Thaksin Shinawatra, ousted in a 2006 coup. Mr Somchai is Thaksin's brother-in-law.

Pressure has built on the army to step in since Mr Somchai rejected military calls to quit, but pro-government forces threaten to take up arms if the elected administration is ousted, raising fears of major civil unrest.

Talks rejected

The founder of PAD said he had rejected a personal plea from the Prime Minister to hold talks on the siege.

Sondhi Limthongkul said demonstrators would not leave until Mr Somchai resigned, adding that the PM should "seek asylum in Myanmar (Burma)".

"Today the Prime Minister contacted me on the telephone to negotiate. There are no talks - if they want to crack down, please don't wait," Sondhi told protesters at Don Mueang airport.

"The Government has asked to negotiate - that means the Government is defeated," he said.